This project examines a series of interrelated processes of intercellular communication in the context of a highly tractable preparation. The mechanisms of stimulus-secretion coupling which appear common to events as disparate as synaptic transmission and exocrine secretion can be studied with high resolution in the model systems provided by intact neuro-glandular preparations and enzymatically isolated giant salivary cells of pulmonate molluscs. These exocrine secretory cells, classically regarded as inexcitable, display all-or-none, overshooting action potentials whose inward current is carried predominantly by calcium. The large cell (approximately 100 micrometers) and secretory granule (approximately 10 micrometers) size allows a direct visual monitoring, in living cells, of exocytotic-like secretory events while cells impaled by microelectrodes. The process of endocytotic membrane recycling can also be examined in living cells using fluorescent extracellular markers. This investigation will examine the relationships between calcium fluxes, electrical coupling and secretion both in isolated cells and in intact glands. The external control of these events will be defined in terms of the already identified central neurons (R and L4, R and L CBI-1) which impinge on these glands.